Semiconductor device

ABSTRACT

The semiconductor device includes a semiconductor element, a first lead, and a second lead. The semiconductor element has an element obverse surface and an element reverse surface spaced apart from each other in a thickness direction. The semiconductor element includes an electron transit layer disposed between the element obverse surface and the element reverse surface and formed of a nitride semiconductor, a first electrode disposed on the element obverse surface, and a second electrode disposed on the element reverse surface and electrically connected to the first electrode. The semiconductor element is mounted on the first lead, and the second electrode is joined to the first lead. The second lead is electrically connected to the first electrode. The semiconductor element is a transistor. The second lead is spaced apart from the first lead and is configured such that a main current to be subjected to switching flows therethrough.

FIELD

The present disclosure relates to a semiconductor device.

BACKGROUND

Heretofore, semiconductor elements using a group III-V nitridesemiconductor (“nitride semiconductor”) such as gallium nitride (GaN)have been developed. JP-A-2012-38885 discloses an example of such asemiconductor element. The semiconductor element disclosed inJP-A-2012-38885 includes a substrate, a nitride semiconductor layerformed on the obverse surface of the substrate, and a plurality ofelectrodes. The electrodes include a source electrode, a drainelectrode, a gate electrode, and a back electrode. The source electrode,the drain electrode, and the gate electrode are disposed on the nitridesemiconductor layer. The back electrode is disposed on the reversesurface of the substrate and is electrically connected to the sourceelectrode via a conductive portion that passes through both thesubstrate and the nitride semiconductor layer.

The above-described semiconductor element constitutes a semiconductordevice together with a plurality of leads and a sealing resin, forexample. The plurality of leads include a source lead, a drain lead, anda gate lead. The source lead is a component on which the semiconductorelement is mounted, and is electrically connected to the back electrode(thus also electrically connected to the source electrode). The drainlead is electrically connected to the drain electrode, and the gate leadis electrically connected to the gate electrode. The sealing resincovers the semiconductor element and the respective leads. Therespective leads are partially exposed from the sealing resin, and theexposed portions are used as external connection terminals. In thissemiconductor device, the source lead is electrically connected to theback electrode and the source electrode, whereby a current circulationpath is formed by the source lead, the source electrode, the conductiveportion, and the back electrode. Part of this circulation path extendsalong the lamination direction of the nitride semiconductor layer.Accordingly, when a current flows through this circulation path,electrons may be trapped in crystal defects in the nitride semiconductorlayer. This may change the properties of the nitride semiconductorlayer, resulting in reduced reliability of the semiconductor element.

SUMMARY

In light of the foregoing, it is an object of the present disclosure toprovide a semiconductor device that can suppress the flow of a currentin the lamination direction of a nitride semiconductor layer.

One aspect of the present disclosure provides a semiconductor deviceincluding: a semiconductor element having an element obverse surface andan element reverse surface that are spaced apart from each other in athickness direction, the semiconductor element including an electrontransit layer that is disposed between the element obverse surface andthe element reverse surface and is formed of a nitride semiconductor, afirst electrode that is disposed on the element obverse surface, and asecond electrode that is disposed on the element reverse surface and iselectrically connected to the first electrode; a first lead on which thesemiconductor element is mounted, the first lead being joined to thesecond electrode; and a second lead that is electrically connected tothe first electrode. The semiconductor element is a transistor, and thesecond lead is spaced apart from the first lead and is configured suchthat a main current to be subjected to switching flows through thesecond lead.

According to the above-described configuration, the first lead to whichthe second electrode is joined and the second lead electricallyconnected to the first electrode are spaced apart from each other.Accordingly, a current circulation path including the first lead, thesecond electrode, the first electrode, and the second lead is notformed. As a result, a current is kept from flowing along the laminationdirection of a nitride semiconductor layer.

Other characteristics and advantages of the present disclosure willbecome more apparent by the following detailed description withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a semiconductor device according toExample 1.

FIG. 2 is a plan view of the semiconductor device shown in FIG. 1.

FIG. 3 is a front view of the semiconductor device shown in FIG. 1.

FIG. 4 is a bottom view of the semiconductor device shown in FIG. 1.

FIG. 5 is a right side view of the semiconductor device shown in FIG. 1.

FIG. 6 is a plan view showing a semiconductor element.

FIG. 7 is a schematic cross-sectional view showing the semiconductorelement.

FIG. 8 is a plan view for illustrating a step in a method for producingthe semiconductor device shown in FIG. 1.

FIG. 9 is a plan view for illustrating another step in the method forproducing the semiconductor device shown in FIG. 1.

FIG. 10 shows a modification of the semiconductor element shown in FIGS.6 and 7.

FIG. 11 is a perspective view showing a semiconductor device accordingto Example 2.

FIG. 12 is a bottom view of the semiconductor device shown in FIG. 11.

FIG. 13 is a perspective view showing a semiconductor device accordingto Example 3.

FIG. 14 is a bottom view of the semiconductor device shown in FIG. 13.

FIG. 15 is a plan view showing a semiconductor device according toExample 4.

FIG. 16 is a schematic cross-sectional view showing a semiconductorelement used in a semiconductor device according to Example 5.

FIG. 17 is a schematic cross-sectional view showing a semiconductorelement used in a semiconductor device according to Example 6.

EMBODIMENTS

The present disclosure will be described in detail by way of variousexamples with reference to the accompanying drawings.

A semiconductor device A1 according to Example 1 will be described withreference to FIGS. 1 to 7. The semiconductor device A1 includes aplurality of leads, a semiconductor element 6, bonding wires 71 to 74,and a sealing resin 8. In the example illustrated in these drawings, theplurality of leads include first to fifth leads 1 to 5. In FIG. 2, thesealing resin 8 is not shown and the outer shape thereof is indicatedwith an imaginary line (double-dot-dash line).

The semiconductor device A1 is surface-mountable on circuit boards ofvarious apparatuses. The semiconductor device A1 has a rectangular shapeas viewed in the thickness direction (z direction). Two directions thatare orthogonal to the z direction and also are orthogonal to each otherare defined as the x direction and the y direction. For example, asshown in FIG. 2, one side of the semiconductor device A1 extends alongthe x direction, and another side of the semiconductor device A1 extendsalong the y direction. The size of the semiconductor device A1 is notparticularly limited, and may be such that, for example, the dimensionin the x direction is about 1 to 10 mm, the dimension in the y directionis about 1 to 10 mm, and the dimension in the z direction is about 0.3to 3 mm.

As described in the following, the leads 1 to 5 support thesemiconductor element 6 and/or are electrically connected to thesemiconductor element 6. The leads 1 to 5 are made of metal, and arepreferably made of either Cu or Ni, or an alloy of Cu and Ni, a 42alloy, or the like. The leads 1 to 5 can be formed through punching,bending, or the like of a metal plate. The leads 1 to 5 each have athickness of 0.08 to 0.5 mm, for example. In the example illustrated inthe drawings, the leads 1 to 5 are each made of Cu and each have athickness of about 0.5 mm.

As shown in FIG. 2, the semiconductor device A1 has two sides that arespaced apart from each other in the y direction (each side extends alongthe x direction). The first lead 1 is disposed closer to one of thesetwo sides (closer to the lower side in FIG. 2). In other words, thefirst lead 1 is disposed closer to the lower side than to the upper sideof the semiconductor device A1. The first lead 1 extends over the entirewidth of the semiconductor device A1 in the x direction.

The second lead 2 and the third lead 3 are provided on sides opposite toeach other in the y direction with respect to the first lead 1. Thesecond lead 2 and the third lead 3 are each spaced apart from the firstlead 1. As shown in FIG. 2, the second lead 2 is adjacent to the lowerside and the left side (extending along the y direction) of thesemiconductor device A1. The third lead 3 is adjacent to the upper sideof the semiconductor device A1 and extends from the left side to theright side (extending along the y direction) of the semiconductor deviceA1. That is, the third lead 3 extends over the entire width of thesemiconductor device A1 in the x direction.

The fourth lead 4 and the fifth lead 5 are provided on the same side asthe second lead 2 in the y direction with respect to the first lead 1.In FIG. 2, the fourth lead 4 and the fifth lead 5 are each providedadjacent to the lower side of the semiconductor device A1. The fourthlead 4 and the fifth lead 5 are spaced apart from each other, and theyare each spaced apart from the first lead 1. The fifth lead 5 isdisposed between the second lead 2 and the fourth lead 4 in the xdirection. That is, the second lead 2, the fifth lead 5, and the fourthlead 4 are spaced apart from each other and disposed in this order inthe x direction.

The dimension of the first lead 1 as viewed in the z direction is largerthan those of the remaining leads 2 to 5. The dimensions of the leads 2to 5 in the x direction are as follows: the dimension of the third lead3 is the largest, and the dimensions of the remaining leads decrease inthe order of the second lead 2, the fourth lead 4, and the fifth lead 5.In the y direction, the distance between the third lead 3 and the firstlead 1 is greater than the distance between the second lead 2 (or thefifth lead 5, the fourth lead 4) and the first lead 1.

The first lead 1 includes a mounting portion 110 and a plurality ofcoupling portions 120. In the example illustrated in the drawings, fourcoupling portions 120 are provided. However, the present disclosure isnot limited thereto.

The mounting portion 110, which is a major portion of the first lead 1,has a rectangular shape as viewed in the z direction. The mountingportion 110 has an obverse surface 111 (FIG. 2) and a reverse surface112 (FIG. 4). The obverse surface 111 and the reverse surface 112 faceaway from each other in the z direction. The obverse surface 111 is asurface that faces upward in FIG. 3 and on which the semiconductorelement 6 is mounted. The reverse surface 112 is a surface that facesdownward in FIG. 3 and is exposed from the sealing resin 8 to serve as aback terminal. The mounting portion 110 has at least one recess 113. Inthe example illustrated in FIG. 4, two recesses 113 (each recess iselongated in the x direction) are formed spaced apart from each other inthe y direction. In FIG. 4, the dimension of the upper recess 113(adjacent to the second lead 2) in the y direction is smaller than thatof the lower recess 113 (adjacent to the third lead). On the other hand,the upper recess 113 and the lower recess 113 have the same dimension inthe x direction. Accordingly, the area of the upper recess 113 as viewedin the z direction is smaller than that of the lower recess 113. Therespective recesses 113 are portions of the mounting portion 110recessed from the reverse surface 112 in the z direction. The thickness(the dimension in the z direction) of each of the portions of themounting portion 110 provided with the recesses 113 is about one-half ofthe thickness of the portion of the mounting portion 110 provided withthe reverse surface 112 (the distance between the obverse surface 111and the reverse surface 112). Each recess 113 is formed by, for example,subjecting the mounting portion 110 (the first lead 1) to half etching.

As shown in FIG. 2, each coupling portion 120 is connected to themounting portion 110 and has a rectangular shape as viewed in the zdirection. In the example illustrated in the drawings, the mountingportion 110 has two end surfaces that are spaced apart from each otherin the x direction and parallel to each other, and two coupling portions120 are disposed on each end surface. Each coupling portion 120 has anobverse surface 121 (FIG. 2), a reverse surface 122 (FIG. 4), and an endsurface 123 (FIGS. 2 and 4). The obverse surface 121 and the reversesurface 122 face away from each other in the z direction. The obversesurface 121 of each coupling portion faces upward in FIG. 3 and is flushwith the obverse surface 111 of the mounting portion. The reversesurface 122 of each coupling portion faces downward in FIG. 3. Thethickness (the dimension in the z direction) of each coupling portion120 is about the same as the thickness of each of the portions of themounting portion 110 provided with the recesses 113. Each couplingportion 120 is formed by, for example, subjecting the first lead 1 tohalf etching. In each coupling portion, the end surface 123 is a surfaceconnecting the obverse surface 121 and the reverse surface 122, facesoutward in the x direction, and is exposed from the sealing resin 8 (seeFIG. 1).

The second lead 2 is disposed at a corner (the lower left corner in FIG.2) of the semiconductor device A1 as viewed in the z direction, andincludes a wire bonding portion 210, two terminal portions 220, and acoupling portion 230.

The wire bonding portion 210 has a rectangular shape elongated in the xdirection as viewed in the z direction. The wire bonding portion 210 hasan obverse surface 211, a reverse surface 212, and a recess 213. Theobverse surface 211 and the reverse surface 212 face away from eachother in the z direction. The obverse surface 211 is a surface thatfaces upward in FIG. 3 and to which the bonding wires 71 are bonded. Thereverse surface 212 is a surface that faces downward in FIG. 3 and isexposed from the sealing resin 8 to serve as a back terminal (see FIG.4). The recess 213 is a portion of the wire bonding portion 210 recessedfrom the reverse surface 212 in the z direction. The thickness (thedimension in the z direction) of a portion of the wire bonding portion210 provided with the recess 213 is about one-half of the thickness of aportion of the wire bonding portion 210 provided with the reversesurface 212. The recess 213 is formed by, for example, subjecting thesecond lead 2 to half etching.

Each terminal portion 220 is connected to the wire bonding portion 210and has a rectangular shape as viewed in the z direction. In the exampleillustrated in the drawings, two terminal portions 220 are disposed onone end surface (end surface that faces away from the semiconductordevice A1) of the wire bonding portion 210 so as to be spaced apart fromeach other in the x direction. Each terminal portion 220 has an obversesurface 221, a reverse surface 222, and an end surface 223. The obversesurface 221 and the reverse surface 222 face away from each other in thez direction. The obverse surface 221 faces upward in FIG. 3. The obversesurface 221 of the terminal portion is flush with the obverse surface211 of the wire bonding portion. The reverse surface 222 faces downwardin FIG. 3. The reverse surface 222 of the terminal portion is flush withthe reverse surface 212 of the wire bonding portion. The end surface 223is a surface connecting the obverse surface 221 and the reverse surface222 and faces outward in the y direction. The reverse surface 212 of thewire bonding portion, the reverse surfaces 222 of the terminal portions,and the end surfaces 223 of the terminal portions are exposed from thesealing resin 8 and connected to each other to function as an externalconnection terminal.

The coupling portion 230 is connected to the outer side of the wirebonding portion 210 in the x direction (the left side in FIG. 2). Thethickness (the dimension in the z direction) of the coupling portion 230is about the same as the thickness of a portion of the wire bondingportion 210 provided with the recess 213. The coupling portion 230 isformed by, for example, subjecting the second lead 2 to half etching.The coupling portion 230 has an obverse surface 231, a reverse surface232, and an end surface 233. The obverse surface 231 and the reversesurface 232 face away from each other in the z direction. The obversesurface 231 faces upward in FIG. 3. The obverse surface 231 of thecoupling portion is flush with the obverse surface 211 of the wirebonding portion. Accordingly, the obverse surface 211 of the wirebonding portion, the obverse surfaces 221 of the terminal portions, andthe obverse surface of the coupling portion 231 together form a flatsurface (see FIG. 2). The reverse surface 232 faces downward in FIG. 3.Of surfaces connecting the obverse surface 231 and the reverse surface232, the end surface 233 is a surface facing in the x direction and isexposed from the sealing resin 8.

In FIG. 2, the third lead 3 is disposed adjacent to the upper side ofthe semiconductor device A1 and extends over the entire width of thesemiconductor device A1 in the x direction. The third lead 3 includes awire bonding portion 310, a plurality of terminal portions 320, and aplurality of coupling portions 330.

The wire bonding portion 310 has a rectangular shape elongated in the xdirection as viewed in the z direction. The wire bonding portion 310 hasan obverse surface 311, a reverse surface 312, and a recess 313. Theobverse surface 311 and the reverse surface 312 face away from eachother in the z direction. The obverse surface 311 faces upward in FIG.3. The obverse surface 311 is a surface to which the bonding wires 72are bonded. The reverse surface 312 faces downward in FIG. 3. Thereverse surface 312 is exposed from the sealing resin 8 to serve as aback terminal. The recess 313 is a portion of the wire bonding portion310 recessed from the reverse surface 312 in the z direction. Thethickness (the dimension in the z direction) of a portion of the wirebonding portion 310 provided with the recess 313 is about one-half ofthe thickness of a portion of the wire bonding portion 310 provided withthe reverse surface 312. The recess 313 is formed by, for example,subjecting the third lead 3 to half etching.

Each terminal portion 320 is connected to the wire bonding portion 310and has a rectangular shape as viewed in the z direction. In the exampleillustrated in FIG. 2, four terminal portions 320 are disposed on oneend surface (end surface that faces away from the semiconductor deviceA1) of the wire bonding portion 310 so as to be spaced apart from eachother in the x direction. Each terminal portion 320 has an obversesurface 321, a reverse surface 322, and an end surface 323. The obversesurface 321 and the reverse surface 322 face away from each other in thez direction. The obverse surface 321 faces upward in FIG. 3. The obversesurface 321 of each terminal portion is flush with the obverse surface311 of the wire bonding portion. The reverse surface 322 faces downwardin FIG. 3. The reverse surface 322 of each terminal portion is flushwith the reverse surface 312 of the wire bonding portion. The endsurface 323 is a surface connecting the obverse surface 321 and thereverse surface 322 and faces outward in the y direction. The reversesurface 312 of the wire bonding portion, the reverse surfaces 322 of theterminal portions, and the end surfaces 323 of the terminal portions areexposed from the sealing resin 8 and connected to each other to functionas an external connection terminal.

In the example illustrated in FIG. 2, two coupling portions 330 areconnected to both ends of the wire bonding portion 310 in the xdirection, respectively. The thickness (the dimension in the zdirection) of each coupling portion 330 is about the same as thethickness of a portion of the wire bonding portion 310 provided with therecess 313. The coupling portions 330 are formed by, for example,subjecting the third lead 3 to half etching. Each coupling portion 330has an obverse surface 331, a reverse surface 332, and an end surface333. The obverse surface 331 and the reverse surface 332 face away fromeach other in the z direction. The obverse surface 331 faces upward inFIG. 3. The obverse surface 331 of each coupling portion is flush withthe obverse surface 311 of the wire bonding portion. Accordingly, theobverse surface 311 of the wire bonding portion, the obverse surfaces321 of the terminal portions, and the obverse surfaces of the couplingportions 331 together form a flat surface (see FIG. 2). The reversesurface 332 faces downward in FIG. 3. Of surfaces connecting the obversesurface 331 and the reverse surface 332, the end surface 333 is asurface facing in the x direction and is exposed from the sealing resin8.

In FIG. 2, the fourth lead 4 is disposed at the lower right corner ofthe semiconductor device A1, and includes a wire bonding portion 410, aterminal portion 420, and a coupling portion 430.

The wire bonding portion 410 has a rectangular shape elongated in the xdirection as viewed in the z direction. The wire bonding portion 410 hasan obverse surface 411, a reverse surface 412, and a recess 413. Theobverse surface 411 and the reverse surface 412 face away from eachother in the z direction. The obverse surface 411 faces upward in FIG.3. The obverse surface 411 is a surface to which the bonding wire 73 isbonded. The reverse surface 412 faces downward in FIG. 3. The reversesurface 412 is exposed from the sealing resin 8 to serve as a backterminal. The recess 413 is a portion of the wire bonding portion 410recessed from the reverse surface 412 in the z direction. The thickness(the dimension in the z direction) of a portion of the wire bondingportion 410 provided with the recess 413 is about one-half of thethickness of a portion of the wire bonding portion 410 provided with thereverse surface 412. The recess 413 is formed by, for example,subjecting the fourth lead 4 to half etching.

The terminal portion 420 is connected to the wire bonding portion 410and has a rectangular shape as viewed in the z direction. The terminalportion 420 is disposed on one end surface (end surface that faces awayfrom the semiconductor device A1) of the wire bonding portion 410. Theterminal portion 420 has an obverse surface 421, a reverse surface 422,and an end surface 423. The obverse surface 421 and the reverse surface422 face away from each other in the z direction. The obverse surface421 faces upward in FIG. 3. The obverse surface 421 of the terminalportion is flush with the obverse surface 411 of the wire bondingportion. The reverse surface 422 faces downward in FIG. 3. The reversesurface 422 of the terminal portion is flush with the reverse surface412 of the wire bonding portion. The end surface 423 is a surfaceconnecting the obverse surface 421 and the reverse surface 422 and facesoutward in the y direction. The reverse surface 412 of the wire bondingportion, the reverse surface 422 of the terminal portion, and the endsurface 423 of the terminal portion are exposed from the sealing resin 8and connected to each other to function as an external connectionterminal.

In FIG. 2, the coupling portion 430 is connected to the right side ofthe wire bonding portion 410 in the x direction. The thickness (thedimension in the z direction) of the coupling portion 430 is about thesame as the thickness of a portion of the wire bonding portion 410provided with the recess 413. The coupling portion 430 is formed by, forexample, subjecting the fourth lead 4 to half etching. The couplingportion 430 has an obverse surface 431, a reverse surface 432, and anend surface 433. The obverse surface 431 and the reverse surface 432face away from each other in the z direction. The obverse surface 431faces upward in FIG. 3. The obverse surface 431 of the coupling portionis flush with the obverse surface 411 of the wire bonding portion.Accordingly, the obverse surface 411 of the wire bonding portion, theobverse surface 421 of the terminal portion, and the obverse surface 431of the coupling portion together form a flat surface (see FIG. 2). Thereverse surface 432 faces downward in FIG. 3. Of surfaces connecting theobverse surface 431 and the reverse surface 432, the end surface 433 isa surface facing in the x direction and is exposed from the sealingresin 8.

In FIG. 2, as viewed in the z direction, the fifth lead 5 is adjacent tothe lower side of the semiconductor device A1 and is disposed betweenthe second lead 2 and the fourth lead 4. The fifth lead 5 includes awire bonding portion 510 and a terminal portion 520.

The wire bonding portion 510 has a rectangular shape elongated in the xdirection as viewed in the z direction. The wire bonding portion 510 hasan obverse surface 511, a reverse surface 512, and a recess 513. Theobverse surface 511 and the reverse surface 512 face away from eachother in the z direction. The obverse surface 511 faces upward in FIG.3. The obverse surface 511 is a surface to which the bonding wires 74are bonded. The reverse surface 512 faces downward in FIG. 3. Thereverse surface 512 is exposed from the sealing resin 8 to serve as aback terminal. The recess 513 is a portion of the wire bonding portion510 recessed from the reverse surface 512 in the z direction. Thethickness (the dimension in the z direction) of a portion of the wirebonding portion 510 provided with the recess 513 is about one-half ofthe thickness of a portion of the wire bonding portion 510 provided withthe reverse surface 512. The recess 513 is formed by, for example,subjecting the fifth lead 5 to half etching.

The terminal portion 520 is connected to the wire bonding portion 510and has a rectangular shape as viewed in the z direction. In FIG. 2, theterminal portion 520 is disposed on one end surface (end surface thatfaces away from the semiconductor device A1) of the wire bonding portion510. The terminal portion 520 has an obverse surface 521, a reversesurface 522, and an end surface 523. The obverse surface 521 and thereverse surface 522 face away from each other in the z direction. Theobverse surface 521 faces upward in FIG. 3. The obverse surface 521 ofthe terminal portion is flush with the obverse surface 511 of the wirebonding portion. The reverse surface 522 faces downward in FIG. 3. Thereverse surface 522 of the terminal portion is flush with the reversesurface 512 of the wire bonding portion. The end surface 523 is asurface connecting the obverse surface 521 and the reverse surface 522,and faces outward in the y direction. The reverse surface 512 of thewire bonding portion, the reverse surface 522 of the terminal portion,and the end surface 523 of the terminal portion are exposed from thesealing resin 8 and connected to each other to function as an externalconnection terminal.

The semiconductor element 6 is a component that performs electricalfunctions of the semiconductor device A1. The semiconductor element 6 isa semiconductor element using a nitride semiconductor. In the presentexample, the semiconductor element 6 is a high electron mobilitytransistor (HEMT) using gallium nitride (GaN). The semiconductor element6 includes an element body 60, first electrodes 61, a second electrode62, third electrodes 63, and fourth electrodes 64.

The element body 60 has an obverse surface 6 a and a reverse surface 6b. As shown in FIG. 3 etc., the obverse surface 6 a and the reversesurface 6 b face away from each other in the z direction. The obversesurface 6 a faces upward in FIG. 3, and the reverse surface 6 b facesdownward in FIG. 3. As shown in FIG. 7, the element body 60 includes asubstrate 601, a buffer layer 602, a first nitride semiconductor layer603, a second nitride semiconductor layer 604, a third nitridesemiconductor layer 605, a protective layer 606, and a conductiveportion 607.

The substrate 601 is, for example, an Si substrate and has apredetermined low resistance value. The thickness (the dimension in thez direction) of the substrate 601 is about 400 to 600 μm. The bufferlayer 602 is formed on the substrate 601 and has a multilayer structurecomposed of a plurality of nitride semiconductor layers. In the exampleillustrated in the drawings, the buffer layer 602 is composed of a firstbuffer layer (which is an AlN film) in contact with the substrate 601and a second buffer layer (which is an AlGaN film) laminated on thefirst buffer layer. The first nitride semiconductor layer 603 is a GaNlayer formed on the buffer layer 602 through epitaxial growth and servesas an electron transit layer. The second nitride semiconductor layer 604is an AlGaN layer formed on the first nitride semiconductor layer 603through epitaxial growth and serves as an electron supply layer. Thetotal thickness (the dimension in the z direction) of the buffer layer602, the first nitride semiconductor layer 603, and the second nitridesemiconductor layer 604 is about 2 μm, which is smaller than thethickness of the substrate 601. Two-dimensional electron gas (2DEG)generated in the vicinity of the interface between the first nitridesemiconductor layer 603 and the second nitride semiconductor layer 604is used as a current flow path.

The third nitride semiconductor layer 605 is a p-type GaN layerlaminated on the second nitride semiconductor layer 604 throughepitaxial growth. The fourth electrodes 64 are formed on the thirdnitride semiconductor layer 605 and functions as gate electrodes. Theprotective film 606 is, for example, an SiN film, and covers the secondnitride semiconductor layer 604, the third nitride semiconductor layer605, and the fourth electrodes 64. A portion of each of the fourthelectrodes 64 is exposed from the protective film 606 (see FIGS. 2 and6). The first electrodes 61 and the third electrodes 63 are formed onthe protective film 606, and portions of the respective first electrodes61 and third electrodes 63 pass through the protective film 606 to be incontact with the second nitride semiconductor layer 604. The firstelectrodes 61 and the third electrodes 63 are spaced apart from eachother (see FIGS. 2 and 6). The first electrodes 61 are formed so as tocover the third nitride semiconductor layer 605 and the fourthelectrodes 64, respectively. The first electrodes 61 function as sourceelectrodes. The third electrodes 63 function as drain electrodes. Asshown in FIGS. 2 and 6, the first electrodes 61, the third electrodes63, and the fourth electrodes 64 are disposed on the obverse surface 6 aof the element.

In response to a voltage signal applied to the fourth electrodes (gateelectrodes) 64, a current (“main current”) flows from the thirdelectrodes (drain electrodes) 63 to the first electrodes 61 (sourceelectrodes). The semiconductor element 6 switches between a state wherethe main current flows and a state where the main current does not flow.That is, the switching element 6 performs switching of the main current.

The second electrode 62 is formed on the reverse surface (the surfacethat faces away from the surface on which the buffer layer 602 isformed) of the substrate 601, and is disposed on the reverse surface 6 bof the element.

Each conductive portion 607 is, for example, a via hole, and passesthrough the second nitride semiconductor layer 604, the first nitridesemiconductor layer 603, and the buffer layer 602 to reach the substrate601. The conductive portion 607 is in contact with the portion of thefirst electrode 61 that passes through the protective film 606 to beelectrically connected to the first electrode 61, and is alsoelectrically connected to the second electrode 62 via the substrate 601.Accordingly, the first electrodes 61 and the second electrode 62 are atthe same potential. The conductive portion 607 may pass through thesubstrate 601 to reach the second electrode 62. The configuration of thesemiconductor element 6 described above is merely an illustrativeexample, and the present disclosure is not limited thereto.

As shown in FIG. 2, the semiconductor element 6 is mounted in a centralportion both in the x direction and the y direction on the obversesurface 111. As shown in FIG. 5, the semiconductor element 6 is mountedon the obverse surface 111 of the first lead 1 in a state where thereverse surface 6 b thereof faces the obverse surface 111 with aconductive bonding material interposed between the reverse surface 6 band the obverse surface 111. With this configuration, the secondelectrode 62 of the semiconductor element 6 is electrically connected tothe first lead 1 via a conductive bonding material. Accordingly, thesecond electrode 62 is at the same potential as the first lead 1. Also,the first electrodes 61 are electrically connected to the secondelectrode 62 via the conductive portions 607, and thus are at the samepotential as the first lead 1.

The plurality of bonding wires 71 are connected to first electrodes 61of the semiconductor element 6 and to the wire bonding portion obversesurface 211 of the second lead 2. With this configuration, the secondlead 2 is electrically connected to the first electrode 61 (sourceelectrode) of the semiconductor element 6 to serve as a source terminal.A main current to be subjected to switching flows through the sourceterminal. The plurality of bonding wires 72 are connected to the thirdelectrodes 63 of the semiconductor element 6 and the wire bondingportion obverse surface 311 of the third lead 3. With thisconfiguration, the third lead 3 is electrically connected to the thirdelectrode 63 (drain electrodes) of the semiconductor element 6 to serveas a drain terminal. The bonding wire 73 is connected to a fourthelectrode 64 of the semiconductor element 6 and the wire bonding portionobverse surface 411 of the fourth lead 4. With this configuration, thefourth lead 4 is electrically connected to a fourth electrode 64 (gateelectrode) of the semiconductor element 6 to serve as a gate terminal.The plurality of bonding wires 74 are connected to a first electrode 61of the semiconductor element 6 and the wire bonding portion obversesurface 511 of the fifth lead 5. With this configuration, the fifth lead5 is electrically connected to the first electrode 61 (source electrode)of the semiconductor element 6 to serve as a source sense terminal. Thesource sense terminal is a terminal for detecting the potential of thefirst electrode 61 (source electrode), and a main current to besubjected to switching does not flow therethrough. Accordingly, thenumber of bonding wires 74 is smaller than the number of bonding wires71 through which a main current to be subjected to switching flows. Thenumbers of the bonding wires 71 to 74 are not limited to the examplesillustrated in the drawings. Instead of the bonding wires 71 to 74,metal plates made of Cu or the like may be used, for example.

The sealing resin 8 covers portions of the respective leads 1 to 5, thesemiconductor element 6, and the bonding wires 71 to 74. The sealingresin 8 is a black epoxy resin, for example.

The sealing resin 8 has an obverse surface 81, a reverse surface 82, andside surfaces 83. The obverse surface 81 and the reverse surface 82 faceaway from each other in the z direction. The obverse surface 81 facesupward in FIG. 3, and the reverse surface 82 faces downward in FIG. 3.The side surfaces 83 are surfaces connecting the obverse surface 81 andthe reverse surface 82 and face in either the x direction or the ydirection. In the example illustrated in the drawings, the side surfaces83 are four flat surfaces each having a rectangular shape. However, thepresent disclosure is not limited thereto.

As shown in FIGS. 1 and 2, the coupling portion end surfaces 123 of thefirst lead 1, the terminal portion end surfaces 223 and the couplingportion end surface 233 of the second lead 2, the terminal portion endsurfaces 323 and the coupling portion end surfaces 333 of the third lead3, the terminal portion end surface 423 and the coupling portion endsurface 433 of the fourth lead 4, and the terminal portion end surface523 of the fifth lead 5 are flush with the side surfaces 83 of thesealing resin 8. Also, the reverse surface 112 of the first lead 1, thewire bonding portion reverse surface 212 and the terminal portionreverse surfaces 222 of the second lead 2, the wire bonding portionreverse surface 312 and the terminal portion reverse surfaces 322 of thethird lead 3, the wire bonding portion reverse surface 412 and theterminal portion reverse surface 422 of the fourth lead 4, and the wirebonding portion reverse surface 512 and the terminal portion reversesurface 522 of the fifth lead 5 are flush with the reverse surface 82 ofthe sealing resin 8.

An example of a method for producing the semiconductor device A1 will bedescribed with reference to FIGS. 8 and 9.

As shown in FIG. 8, a lead frame 10 is prepared. The lead frame 10 is aplate-shaped material that is to be processed into leads 1 to 5. Anobverse surface 1010 of the lead frame 10 is a surface that is processedinto the obverse surface 111 and the coupling portion obverse surfaces121 of the first lead 1, the wire bonding portion obverse surface 211,the terminal portion obverse surfaces 221, and the coupling portionobverse surface 231 of the second lead 2, the wire bonding portionobverse surface 311, the terminal portion obverse surfaces 321, and thecoupling portion obverse surfaces 331 of the third lead 3, the wirebonding portion obverse surface 411, the terminal portion obversesurface 421, and the coupling portion obverse surface 431 of the fourthlead 4, and the wire bonding portion obverse surface 511 and theterminal portion obverse surface 521 of the fifth lead 5. The respectiveportions of the obverse surface 1010 of the lead frame 10 are flush witheach other. In FIG. 8, two types of hatching patterns with differentline densities are applied to the lead frame 10. Regions with arelatively dense hatching pattern are regions with a greater thickness(the dimension in the z direction). On the other hand, regions with arelatively sparse hatching pattern are regions with a smaller thickness(the dimension in the z direction). These regions are formed by, forexample, subjecting the lead frame 10 to half etching. The base materialof the lead frame 10 is Cu, for example. However, the present disclosureis not limited thereto.

Next, as shown in FIG. 9, the semiconductor element 6 is bonded to amounting portion 110 of the lead frame 10 using a conductive bondingmaterial. Thereafter, the bonding wires 71 to 74 are bonded to therespective electrodes of the semiconductor element 6 and the lead frame10. Subsequently, a resin material is hardened to form a sealing resin(not shown) that covers portions of the lead frame 10, the semiconductorelement 6, and the bonding wires 71 to 74. This sealing resin is formedover the entire region shown in FIG. 9, for example. Then, the leadframe 10 and the sealing resin are cut along a cutting line 1020. As aresult, the above-described semiconductor device A1 is obtained.

Next, functions and effects of the semiconductor device A1 will bedescribed.

As described above, in the semiconductor device A1, the second electrode62 of the semiconductor element 6 is connected to the first lead 1, andthe first electrodes 61 are connected to the second lead 2 via thebonding wires 71. That is, the semiconductor element 6 is connected toboth the first lead 1 and the second lead 2. On the other hand, thefirst lead 1 and the second lead 2 are spaced apart from each other.With this configuration, a current circulation path including the firstlead 1, the second electrode 62, the conductive portions 607, the firstelectrodes 61, the bonding wires 71, and the second lead 2 is notformed. Accordingly, a current is kept from flowing along the laminationdirection (z direction) of the second nitride semiconductor layer 604and the first nitride semiconductor layer 603. As a result, undesirablechanges in properties of the second nitride semiconductor layer 604 andthe first nitride semiconductor layer 603 are suppressed, whichcontributes to improvement in the long-term reliability of thesemiconductor element 6.

In the semiconductor device A1, the separation distance between thethird lead 3 and the first lead 1 is greater than the separationdistance between the second lead 2 (or the fifth lead 5 and the fourthlead 4) and the first lead 1. Such a configuration helps to increase thedielectric strength between the first lead 1 and the third lead 3, towhich a relatively high voltage is applied.

In the semiconductor device A1, the reverse surface 112 of the firstlead 1 is exposed from the reverse surface 82 of the sealing resin 8.With this configuration, the first lead 1 functions as a back terminalwhen the semiconductor device A1 is mounted on a circuit board or thelike, and also functions as a heat dissipator for dissipating heatgenerated by the semiconductor element 6.

The semiconductor device A1 includes the fifth lead 5 in addition to thesecond lead 2. With this configuration, the semiconductor device A1 canhave, in addition to a source terminal (the second lead 2) through whicha main current to be subjected to switching flows, a source senseterminal (the fifth lead 5 through which a main current does not flow)for detecting the electric potential of the source electrodes (the firstelectrodes 61). Also, by setting the number of bonding wires 71connected to the second lead 2 to be larger than the number of bondingwires 74 connected to the fifth lead 5, the resistance to a current thatflows via the second lead 2 can be set low. Also, the number of terminalportions 220 of the second lead 2 is larger than the number of terminalportions 520 of the fifth lead 5, and the second lead 2 has a largerdimension in the x direction than the fifth lead 5 does. With such aconfiguration, the cross-sectional area of the current path can berelatively increased, whereby the resistance to a current that flowsthrough the second lead 2 can be reduced.

Although an example where the semiconductor element 6 is a HEMT has beendescribed above, the present disclosure is not limited thereto. Theconfiguration of the semiconductor element 6 is not limited as long asthe first electrodes 61 disposed on the obverse surface 6 a and thesecond electrode 62 disposed on the reverse surface 6 b are electricallyconnected to each other via the conductive portions 607. The conductiveportion 607 is not limited to a via hole as long as it allows electricalcommunication between the first electrode 61 and the second electrode62. For example, as shown in FIG. 10, the conductive portion 607 may beformed on a side surface of the element body 60.

In the above-described example, the coupling portion end surfaces 123 ofthe first lead 1, the terminal portion end surfaces 223 and the couplingportion end surface 233 of the second lead 2, the terminal portion endsurfaces 323 and the coupling portion end surfaces 333 of the third lead3, the terminal portion end surface 423 and the coupling portion endsurface 433 of the fourth lead 4, and the terminal portion end surface523 of the fifth lead 5 are flush with the side surfaces 83 of thesealing resin 8. However, the present disclosure is not limited thereto.These end surfaces may protrude from the side surfaces 83 or may berecessed inward from the side surfaces 83. Each of the end surfaces maybe flat, curved, or have recesses and protrusions.

A semiconductor device A2 according to Example 2 will be described withreference to FIGS. 11 and 12. In these drawings, components that areidentical or similar to those of the above-described semiconductordevice A1 are given the same reference signs, and redundant explanationsthereof are omitted as appropriate.

In the semiconductor device A2, the shape of a first lead 1 is differentfrom that in the semiconductor device A1. In the semiconductor deviceA2, a surface of the first lead 1 that faces away from an obversesurface 111 does not have a portion corresponding to the reverse surface112 in Example 1, and the entire surface forms a recess 113 (or it canbe said that the surface is not provided with a recess and is entirelyflat). Accordingly, a mounting portion 110 is not exposed from a reversesurface 82 of a sealing resin 8. Further, the first lead 1 includesterminal portions 130 instead of the coupling portions 120. Eachterminal portion 130 has an obverse surface 131, a reverse surface 132,and an end surface 133. The obverse surface 131 and the reverse surface132 face away from each other in the z direction. The obverse surface131 faces upward in FIG. 11. The obverse surface 131 of the terminalportion and the obverse surface 111 are flush with each other. Thereverse surface 132 of each terminal portion faces downward in FIG. 11.The thickness (the dimension in the z direction) of each terminalportion 130 is about twice as great as that of the mounting portion 110,and the reverse surface 132 of each terminal portion is exposed from thereverse surface 82 of the sealing resin 8. The end surface 133 of theterminal portion is a surface connecting the obverse surface 131 and thereverse surface 132, and faces outward in the x direction. The reversesurface 132 and the end surface 133 are exposed from the sealing resin 8and connected to each other to function as a terminal.

Also, in the semiconductor device A2, the first lead 1 and the secondlead 2 are spaced apart from each other. Accordingly, a currentcirculation path, which has conventionally been a problem, is notformed, whereby a current is kept from flowing along the laminationdirection (z direction) of nitride semiconductor layers 603 and 604.This improves the long-term reliability of the semiconductor element 6.

In the semiconductor device A2, the first lead 1 includes, as terminals,the terminal portions 130 exposed from the sealing resin 8. Eachterminal portion 130 is a terminal configured such that it has the endsurface 133 exposed from a side surface 83 of the sealing resin and thereverse surface 132 exposed from the reverse surface 82 of the sealingresin and the end surface 133 and the reverse surface 132 are connectedto each other. When the semiconductor device A2 is mounted on a circuitboard, these terminals are joined to circuit wiring formed on thecircuit board through soldering. Since solder fillets are formed on theend faces 133 of the terminal portions, whether the terminal portions130 are joined to the circuit wiring can be visually confirmed.

A semiconductor device A3 according to Example 3 will be described withreference to FIGS. 13 and 14. In these drawings, components that areidentical or similar to those of the above-described semiconductordevice A1 are given the same reference signs, and redundant explanationsthereof are omitted as appropriate.

In the semiconductor device A3, the shape of a first lead 1 is differentfrom that in the semiconductor device A1. The first lead 1 of thesemiconductor device A3 includes terminal portions 130 that are similarto those in the semiconductor device A2. The configuration of theterminal portions 130 is similar to that of the terminal portions 130 inExample 2. In the semiconductor device A3, reverse surfaces 132 of theterminal portions are flush with a reverse surface 112. The reversesurface 112, the reverse surfaces 132 of the terminal portions, and endsurfaces 133 of the terminal portions are exposed from a sealing resin 8and connected to each other to function as terminals.

Also, in the semiconductor device A3, the first lead 1 and a second lead2 are spaced apart from each other, and a current circulation path isthus not formed. Accordingly, a current is kept from flowing along thelamination direction (z direction) of nitride semiconductor layers 603and 604, which improves the long-term reliability of a semiconductorelement 6.

In the semiconductor device A3, the first lead 1 has the terminalportions 130 exposed from the sealing resin 8 and the reverse surface112 is exposed from a reverse surface 82 of the sealing resin 8.Accordingly, the joined state of the first lead 1 can be checked basedon the appearance thereof after mounting the semiconductor device A3 ona circuit board, and further, the first lead 1 can also function as aheat dissipator for dissipating heat generated by the semiconductorelement 6.

A semiconductor device A4 according to Example 4 will be described withreference to FIG. 15. In FIG. 15, components that are identical orsimilar to those of the above-described semiconductor device A1 aregiven the same reference signs, and redundant explanations thereof areomitted. In FIG. 15, for the sake of convenience in understanding, asealing resin 8 is not shown and the outer shape thereof is indicatedwith an imaginary line (double-dot-dash line).

The semiconductor device A4 is different from the semiconductor deviceA1 in that it does not include a source sense terminal (fifth lead 5). Asecond lead 2 of the semiconductor device A4 extends to a position neara fourth lead 4 in the x direction, and includes three terminal portions220. The semiconductor device A4 may also be configured such that thesecond lead 2 is the same as the second lead 2 in the semiconductordevice A1 and does not include the fifth lead 5 in the semiconductordevice A1.

Also, in the semiconductor device A4, a first lead 1 and the second lead2 are spaced apart from each other, and a current circulation path isthus not formed. Accordingly, a current is kept from flowing along thelamination direction (z direction) of nitride semiconductor layers 603and 604, which improves the long-term reliability of a semiconductorelement 6.

A semiconductor device A5 according to Example 5 will be described withreference to FIG. 16. In FIG. 16, components that are identical orsimilar to those of the above-described semiconductor device A1 aregiven the same reference signs, and redundant explanations thereof areomitted as appropriate.

The semiconductor device A5 is different from the semiconductor deviceA1 in that a semiconductor element 6 is configured such that conductiveportions 607 are in contact with third electrodes 63 instead of withfirst electrodes 61 and electrically connected to the third electrodes63. In the semiconductor device A5, the conductive portions 607 areelectrically connected to the third electrodes 63 and also electricallyconnected to a second electrode 62 via a substrate 601. Accordingly, thethird electrodes 63 and the second electrode 62 are at the samepotential. The second electrode 62 of the semiconductor element 6 iselectrically connected to a first lead 1 using a conductive bondingmaterial. Accordingly, the second electrode 62 of the semiconductorelement 6 is at the same potential as the first lead 1. The thirdelectrodes 63 are electrically connected to the second electrode 62 viathe conductive portions 607 and thus are at the same potential as thefirst lead 1.

In the semiconductor device A5, the first lead 1 and the third lead 3are spaced apart from each other. Accordingly, even if the secondelectrode 62 of the semiconductor element 6 is connected to the firstlead 1 and if the third electrodes 63 and the third lead 3 are connectedby bonding wires 72, a current circulation path including the first lead1, the second electrode 62, the conductive portions 607, the thirdelectrodes 63, the bonding wires 72, and the third lead 3 is not formed.Accordingly, a current is kept from flowing along the laminationdirection (z direction) of a second nitride semiconductor layer 604, afirst nitride semiconductor layer 603, and a buffer layer 602, whichimproves the long-term reliability of the semiconductor element 6.

A semiconductor device A6 according to Example 6 will be described withreference to FIG. 17. In FIG. 17, components that are identical orsimilar to those of the above-described semiconductor device A1 aregiven the same reference signs, and redundant explanations thereof areomitted as appropriate.

In the semiconductor device A6, a semiconductor element 6 does notinclude a conductive portion 607, and first electrodes 61 and a firstlead 1 are connected to each other by bonding wires 75. The bondingwires 75 are connected to the first electrodes 61 of the semiconductorelement 6 and an obverse surface 111 of the first lead 1. With thisconfiguration, the first lead 1 is at the same potential as the firstelectrodes 61 of the semiconductor element 6. A second electrode 62 isconnected to the first lead 1 using a conductive bonding material, andis at the same potential as the first lead 1. Accordingly, the firstelectrodes 61 and the second electrode 62 are electrically connected toeach other and are at the same potential.

Also, in the semiconductor device A6, the first lead 1 and a second lead2 are spaced apart from each other, and a current circulation path,which has conventionally been a problem, is not formed. Accordingly, thesemiconductor device A6 can exhibit effects similar to those in Example1.

The semiconductor device according to the present disclosure is notlimited to the above-described examples. Various modifications in designmay be made freely in the specific structure of each part of thesemiconductor device according to the present disclosure.

1. A semiconductor device comprising: a semiconductor element having anelement obverse surface and an element reverse surface that are spacedapart from each other in a thickness direction, the semiconductorelement including: an electron transit layer that is disposed betweenthe element obverse surface and the element reverse surface and isformed of a nitride semiconductor; a first electrode that is disposed onthe element obverse surface; and a second electrode that is disposed onthe element reverse surface and is electrically connected to the firstelectrode; a first lead on which the semiconductor element is mounted,the first lead being joined to the second electrode; and a second leadthat is electrically connected to the first electrode, wherein thesemiconductor element is a transistor, and the second lead is spacedapart from the first lead and allows passage of a main current to besubjected to switching flows.
 2. The semiconductor element according toclaim 1, further comprising a sealing resin that covers thesemiconductor element, wherein the first lead has a surface that islocated opposite to the semiconductor element and is exposed from thesealing resin.
 3. The semiconductor element according to claim 1,further comprising a third lead and a fourth lead, wherein thesemiconductor element has a third electrode and a fourth electrodedisposed on the element obverse surface, the third lead is electricallyconnected to the third electrode, and the fourth lead is electricallyconnected to the fourth electrode.
 4. The semiconductor elementaccording to claim 3, wherein, as viewed in the thickness direction, thesecond lead and the third lead are disposed opposite to each other withrespect to the first lead.
 5. The semiconductor element according toclaim 4, wherein, as viewed in the thickness direction, a separationdistance between the first lead and the third lead is greater than aseparation distance between the first lead and the second lead.
 6. Thesemiconductor element according to claim 3, wherein, as viewed in thethickness direction, the third lead and the fourth lead are disposedopposite to each other with respect to the first lead.
 7. Thesemiconductor element according to claim 3, further comprising a fifthlead that is electrically connected to the first electrode and is at asame potential as the first electrode.
 8. The semiconductor elementaccording to claim 7, further comprising: a plurality of first wiresthat connect the first electrode and the second lead; and at least onesecond wire that connects the first electrode and the fifth lead,wherein the first wires are greater in number than the at least onesecond wire.
 9. The semiconductor device according to claim 7, wherein,as viewed in the thickness direction, the fifth lead is disposed betweenthe second lead and the fourth lead.
 10. The semiconductor deviceaccording to claim 3, further comprising: at least one wire thatconnects the third electrode and the third lead; and at least one wirethat connects the fourth electrode and the fourth lead.
 11. Thesemiconductor device according to claim 3, wherein, as viewed in thethickness direction, the third lead is elongated along a firstdirection, and a dimension of the second lead in the first direction issmaller than a dimension of the third lead in the first direction andlarger than a dimension of the fourth lead in the first direction. 12.The semiconductor device according to claim 3, wherein the firstelectrode is a source electrode, the third electrode is a drainelectrode, and the fourth electrode is a gate electrode.
 13. Thesemiconductor device according to claim 1, wherein the semiconductorelement includes: a substrate that is disposed between the electrontransit layer and the element reverse surface; an electron supply layerthat is disposed between the electron transit layer and the elementobverse surface and is formed of a nitride semiconductor; and aconductive portion that passes through the electron transit layer andthe electron supply layer to allow electrical communication between thefirst electrode and the second electrode.
 14. The semiconductor deviceaccording to claim 1, further comprising a wire that connects the firstelectrode and the first lead.
 15. The semiconductor device according toclaim 1, wherein the electron transit layer is made of GaN.